Research On Algorithm For Transient Stability Assessment Of Power System With Stability Measures

With the worldwide trends in deregulation and open access of power systems,modern interconnected power systems might be more often operated close to itstransient stability limits than before. To prevent cascading outages, safe operationlimits for all the credible situations and fault conditions should be satisfied. However,in some weak parts of the power network, when subjected to a severe disturbance,power system may lose synchronism even though modern protection apparatus canclear faults quickly. Therefore stability control measures such as stream turbinefast-valving, generator tripping, load shedding and combinations of several abovemeasures are adopted for enhancing the capability of power transmission. In recentyears, hybrid methods combining time-domain simulation with transient energyfunction analysis have been widely applied for transient stability assessment (TSA).As the conventional hybrid methods have not considered the TSA for cases includingstability measures, there is the need for developing approaches for these cases. The paper applies the Normalized Transient Energy Function (NTEF) to the TSAin power engineering for power systems including stability measures. New methodcalled sample-ruler technique has been developed to evaluate the energy margin ofcontingencies for cases with stability measures. This technique avoids the reinsertpseudo fault on trajectory simulation and made the assessment of transient stabilitymargin incorporate with a commercial simulation software package easily. With the new approach, a transient stability strategy for assessment of NTEFstability margin is developed. It can screen out harmless faults rapidly, and evaluatethe Normalized Transient Energy Margins (NTEM) for harmful and potentiallyharmful faults of power systems. For comparing stability degree among the harmfuland potentially harmful disturbances, the NTEM is further converted into TransientStability Time Margin (TTM). The concept of TTM is easier to be accepted by systemoperators. It is used in ordering disturbances according to their harm to systemsecurity in the sense of system stability. The paper also presents a novel computation strategy for Power TransmissionLimit (PTL). On the basis of sensitivity analysis of TTM, the generators of sendingside and loads of receiving side are both concerned with the PTL assessment. Case studies on the real power network are presented to verify the effectivenessand efficiency of the new strategies.